The present invention relates to a method of shading paper that comprises or consists of one or more layers made of the same or different pulps, which paper is intended to be used in connection with foodstuffs.
The invention also relates to a color mixture for shading paper that consists of one or more layers made of the same or different pulps, which paper is intended to be used in connection with foodstuffs, and a shaded paper produced by the method, using the color mixture.
So as to obtain the desired optical properties in paper products, the paper industry has used "shading colors". However, it has not been possible to use the shaded paper products in a satisfactory way for packaging in the foodstuffs industry, as many of the colors used are not approved by the U.S. Food and Drug Administration, the FDA. It has therefore not been possible to use the desired combinations of colors. In particular, a violet color approved by the FDA has been lacking.
The coloring of paper differs considerably from the shading of paper since with coloring the intention is for the product to acquire the same color as the pigment or pigment mixture, whereas with shading the intention is to reduce the natural yellow hue of the paper and the goal is to obtain an uncolored final product. How uncolored the final product becomes is measured by its whiteness and can be expressed by values for the color coordinate b*. A more uncolored product has greater whiteness than a product in which some nuance of color can be detected. Shading can thus be defined as "decoloring". Natively paper has a yellow color that is caused by inter alia residual lignin. Lignin is a natural constituent in paper products. When shading paper, a special color mixture of predetermined composition is added to reduce the reflection of green light and red light in the paper and thereby obtain a whiter product. Many dyestuffs have considerable light absorbency in blue light and this makes them unusable for increasing the whiteness of the paper.
A purpose of the invention is to provide a method, and a color mixture for shading paper products which enables the paper products shaded as desired to be used in the foodstuffs industry also, for packaging foodstuffs, and a shaded paper for such use.
Following extensive investigations it has been shown, surprisingly, that using the FDA-approved violet color quinacridone red as a main component, typically in a quantity of 50 per cent or more and particularly between about 75-85% (e.g. about 80%), in a color mixture that contains at least one further FDA-approved color for optical cooperation with the primary component, results in paper products that, when shaded with such a color mixture, display enhanced whiteness compared with the unshaded paper product.
According to the invention the method is characterized in that a pulp or layer, and more pulps or layers respectively, are treated with a color mixture of at least two optically cooperating dyestuffs that are approved for foodstuffs, one of which is quinacridone red with the FDA registration data C.I. pigment violet 19, C.I. No. 73900 (Code of Federal Regulations, Food and Drugs, Title 21, Part 170-199), and constituting the primary component in the color mixture, in order to obtain a shaded paper with a value for the color coordinate b* that is between 0 and 3, or any narrower range within that broad range (e.g. between about 0.2 and 1.5).
According to the invention the color mixture is characterized in that it contains at least two optically cooperating dyestuffs that are approved for foodstuffs, one of which is quinacridone red with the FDA registration data C.I. pigment violet 19, C.I. No. 73900 (Code of Federal Regulations, Food and Drugs, Title 21, Part 170-199), and constituting the primary component in the color mixture, which produces a shaded paper with a value for the color coordinate b* that is between 0 and 3.
According to a currently most preferred embodiment of the invention the treatment is carried out with a color mixture containing the above violet quinacridone red and phthalocyanine blue with the FDA registration data C.I. pigment blue 15, 15:1, 15:2, 15:3 and 15:4, C.I. No. 74160, CAS Reg. No. 147-14-8 (Code of Federal Regulations, Food and Drugs, Title 21, Part 170-199).
The term "paper" also refers to cardboard. Examples of pulps that can be used are CTMP (Chemical Thermo Mechanical Pulp), and chemical pulps, such as kraft pulp. When used in a packaging material for foodstuffs, the paper may be coated with a barrier of polythene, for instance, but in many cases it can be used without such a barrier so that the foodstuff, which may be solid or liquid, comes into direct contact with the shaded paper.
According to one aspect of the present invention, a method of shading paper for use in connection with foodstuffs, and having at least one layer of pulp, is provided comprising: (a) Treating the at least one layer, or the pulp before formed into the paper layer, with a color mixture of at least two optically cooperating pigments that are approved for foodstuffs, the primary component of the color mixture comprising quinacridone red with the FDA registration data C.I. pigment violet 19, C.I. No. 73900 (Code of Federal Regulations, Food and Drugs, Title 21, Part 170-199), so as to obtain a shaded paper with a value for the color coordinate b* that is between 0 and 3. Preferably (a) is practiced using a color mixture in which the primary component comprises more than 50 per cent of the color mixture, preferably between about 75-85 per cent, and most preferably about 80 per cent. Also preferably (a) is practiced using a color mixture, calculated on pigment content, with a dosage of between about 10-500 (preferably between about 30-300) grams per ton of paper or pulp.
In the preferred embodiment (a) is carried out with a color mixture that also contains at least one blue pigment approved for foodstuffs, such as a mixture consisting essentially of the primary component and at least one blue pigment. The preferred blue pigment is phthalocyanine blue with the FDA registration data C.I. pigment blue 15, 15:1, 15:2, 15:3 and 15:4, C.I. No. 74160, CAS Reg. No. 147-14-8 (Code of Federal Regulations, Food and Drugs, Title 21, Part 170-199).
In effecting the invention, (a) may be practiced by adding the color mixture to the pulp prior to formation of the paper layer, and the color mixture may be added to two or more different pulps, or two different batches of the same pulp which is made into multiple layers. A preferred pulp is CTMP.
The method may further comprise (b) providing a barrier coating on the shaded paper, and bringing the barrier coating into contact with solid or liquid foodstuffs. Alternatively the method may further comprise (c) bringing the shaded paper directly into contact with solid or liquid foodstuffs, e.g. by packaging the foodstuff with the paper.
According to another aspect of the present invention a shaded paper having at least one layer, and for use in connection with foodstuffs is provided. The at least one layer is colored with a color mixture of at least two optically cooperating pigments that are approved for foodstuffs, the primary component of the color mixture comprising quinacridone red with the FDA registration data C.I. pigment violet 19, C.I. No. 73900 (Code of Federal Regulations, Food and Drugs, Title 21, Part 170-199), so as to obtain a shaded paper with a value for the color coordinate b* that is between 0 and 3. The details of the color mixture in the paper, including the percentage of the color mixture that the primary component comprises, the dosage, and other preferred dyes, are as described above.
According to yet another aspect of the present invention a color mixture per se is provided comprising or consisting essentially of at least two optically cooperating pigments that are approved for foodstuffs, the primary component of the color mixture comprising quinacridone red with the FDA registration data C.I. pigment violet 19, C.I. No. 73900 (Code of Federal Regulations, Food and Drugs, Title 21, Part 170-199), capable of obtaining, when applied to a paper layer or pulp, shaded paper with a value for the color coordinate b* that is between 0 and 3. The details of the pigments, the percentage of the primary component, and the like, also may be as provided above.
It is the primary object of the present invention to effectively produce shaded paper for use in connection with foodstuffs, including direct contact therewith, with a value for the color coordinate b* that is between zero and 3 (or a narrower range within that broad range). This and other objects of the invention will become clear from an inspection of the detailed description which follows, and the appended claims.